To render a surface of any nature touch-sensitive by making it possible to locate a press on a surface, the known solutions come mainly under two approaches, namely the deployment of a capacitive film or the laying of an infrared frame on the surface.
In the solutions based on the use of a capacitive film, a film composed of an electrical network etched on the latter and linked to electronics is deployed and glued on the surface to be touch-sensitized. When the surface is touched with a finger, the capacitance which is measured is modified, making it possible to locate the interaction. The drawback of this approach is that it is not compatible with an element other than the finger, making it difficult for example to wear gloves. Moreover, the deployment of such a film renders visible a network of wires printed on the latter, decreasing the transparency of the surface.
The solutions based on infrared (IR) technology use a frame composed of infrared light-emitting diodes (LEDs) laid on the surface and forming a gridwork of emitting and receiving rows. When a finger or any other object cuts off the horizontal and vertical beams, it is located. This technology is very sensitive to sunlight which is highly laden with infrared, as well as to the environment such as the degree of dirtiness of the surface. Moreover, the infrared frame is in general cup-like, this hampering the general design and the use of diverse surfaces.
An additional drawback which is common to the known approaches, is the cost of implementation which is very high and evolves exponentially as a function of the size of the surface to be touch-sensitized.
Moreover, other touch-sensitizing technologies exist based on the measurement of load with the help of strain gauges or pressure sensors. The interaction point is determined by considering the distribution of the loads and by associating it with the barycenter of the sensors weighted by the respective measured pressures. U.S. Pat. No. 3,657,475 proposes a device using three sensors to determine the point of pressure on a plate. However, these solutions are applicable only to small-size surfaces, that is to say those whose size does not exceed that of the conventional screens of personal computers or tablets.
Moving to more significant surfaces generates problems as regards the rigidity of the plate and the deformation of the surface under the application of an interaction force.
Moreover, an apparent lack of rigidity of a surface does not afford the user a good feeling during a touch.
To alleviate the problems related to the rigidity of the surface, it is possible to increase the number of sensors so as to improve its holding. However, the use of more than four sensors increases the degree of hyperstatism of the system and it is no longer possible to deduce an analytical equation by applying the principle of statics to determine the location of the touch.
Thus, no solution suitable for locating an interaction on a large-size surface exists in the prior art.
The present invention addresses this need by alleviating the drawbacks of the existing approaches.